(1) Increased CSF concentrations of phosphotau protein, tau protein phosphorylated at threonine 231, were shown to be an effective biomarker for distinguishing patients with Alzheimer disease from age-matched controls and patients with geriatric major depression. (2): The brain is protected from edema by an intact blood-brain barrier. Damaging this barrier allows plasma salts and protein into brain, accompanied by water, with a resultant edema. This damage occurs following stroke and brain ischemia.